The present disclosures relate to hermetically sealed tank systems.
An internal combustion engine for a vehicle such as an automobile communicates with a fuel tank. In particular, in such vehicles, a canister which communicates with the fuel tank is known in the art. The canister contains adsorbent materials to adsorb fuel vapor in order to prevent the fuel vapor from diffusing into the atmosphere outside of the fuel tank. More specifically, the canister communicates with the space above the liquid level in the fuel tank. The canister captures the fuel vapor from this space when the gas within the fuel tank containing the fuel vapor is exhausted into the canister, so that only the air is discharged into the atmosphere.
Recently, in order to more reliably prevent fuel vapor from diffusing into the atmosphere, a hermetically sealed tank system having a fuel tank with a hermetically sealed structure has been introduced (for example, Japanese Laid-Open Patent Publication No. 2003-35231). In such a hermetically sealed tank system, the space above the liquid level in the fuel tank communicates with a canister via a vapor passage. The fuel tank is hermetically sealed when a closing valve provided in this vapor passage is closed. The closing valve is opened only when the conditions for opening the valve are met at a certain point in time, e.g. during oil feeding. When the closing valve is opened, the fuel vapor in the fuel tank is able to be exhausted into the canister via the vapor passage.
In a typical fuel tank, there is a fuel supply device for feeding fuel in the fuel tank to an internal combustion engine. Such a fuel supply device conventionally comprises a fuel pump, a fuel filter and pressure regulating valve etc. The fuel filter is configured to filter the fuel drawn into the fuel pump. The fuel pump pumps the fuel to the internal combustion engine. The pressure regulating valve regulates the pressure of the fuel (fuel pressure) supplied from the fuel pump to the internal combustion engine. In such devices, a diaphragm valve with a diaphragm is widely used as a pressure regulating valve. The diaphragm of the diaphragm valve partitions the interior space of the diaphragm valve into a pressure regulating chamber and a backpressure chamber. The diaphragm valve is configured to regulate the fuel pressure in the pressure regulating chamber in accordance with the fluid pressure in the backpressure chamber. Typically, the backpressure chamber communicates with the fuel tank, and more specifically with the aforementioned space above the liquid level in the fuel tank. As a result, due to the communication, the pressure within the backpressure chamber equalizes to become the same as the pressure in the space above the liquid level, i.e., the internal pressure of the fuel tank. In this way, the pressure regulating valve regulates the fuel pressure using the internal pressure of the fuel tank.
The space above the liquid level in the fuel tank perpetually communicates with the atmosphere via a canister if the fuel tank is configured in a non-hermetically sealed type configuration. Thus, the internal pressure of the fuel tank equalizes to the ambient pressure. Consequently, the pressure within the backpressure chamber of the pressure regulating valve is also maintained at atmospheric pressure when the fuel supply device is actuated. As a result, the pressure of the fuel supplied to an internal combustion engine can be regulated at a predetermined preset pressure relative to the ambient pressure.
On the other hand, in a hermetically sealed tank system, the fuel tank is typically hermetically sealed except for occasional opening of a limited duration. Therefore, the internal pressure of the fuel tank may be higher or lower than the atmospheric pressure, in contrast to the fuel tank described above. If the fuel supply device is driven in such conditions, the pressure in the backpressure chamber of the pressure regulating valve can consequently also be higher or lower than the ambient pressure. Accordingly, the fuel pressure regulated by the pressure regulating valve may vary in accordance with the pressure in the backpressure chamber. As a result, the fuel pressure deviates from the preset pressure value.
In this context, a hermetically sealed tank system is desired that includes a pressure regulating valve capable of regulating the fuel pressure on the basis of the ambient pressure, without being affected by the internal pressure in the fuel tank.